2001 Yamahe 250 OX 66 problem. Need help.

[ladygrady]

I am only able to get 4000 RPM out of the one motor and the other motor gets up to 5700 RPM. Once we get over the 4000 RPM there is no more power when the throttle is pushed down. If you keep changing the RPMs when running, the RPMs are all over the place sometimes dropping over 2000 RPM. When running at 3800 RPM the engine run fine except for every once in a while the PRM will drop to 2200 and then back up again within seconds. Had the engine looked at and the ground for one of the coils was bad, it was fixed. Ran the boat again and had the same problem. Found that one of the fittings on the gas tank was leaking air and we had all the fittings replaced.

Ran the boat again and still had the problem. The O2 sensor was looked at and was clogged. Cleaned out the dumb bell and ran the boat and still have the problem. I de-carbed the engine and now only can get 2000 RPM out of the motor.

What should I do next? I don't want to keep throwing money at the thing and would like to find a way to diagnose the problem.

[ladygrady]

?

Anyone have any ideas?

[boats.net]

Start with a compression test. Run fuel vacumn and fuel pressure tests to see if have fuel restriction or loss of fuel pressure.

[Basthumb]

We switched the o2 sensors between motors and the problem went away.

[jb123]

have you cleaned vst filter and sump lately?

if youre only getting 2k do your gauges show any errors or buzzer buzzin?